1. Field of the Invention
The present invention relates to a mobile radiotelephone for data communication, and more particularly, to means for notifying the operator of the mobile radiotelephone of the completion of data communication.
2. Description of the Prior Art
In performing data communication by means of a mobile radiotelephone by using radio waves in a voice frequency band, first the operator picks up the handset to set the telephone set in an off-hook state, and dials the telephone number of the called party. Then, the telephone set of the called party rings. Then, the called party picks up the handset, and thereby the speaking circuit is connected. After the speaking circuit has been connected, a conversational mode or a speech communication mode is established.
When data communication is desired, the operator operates a changeover switch or the like to connect the speech signal line of the mobile radiotelephone set to a data MODEM, and thereby the conversational mode is changed for a data communication mode, in which the telephone sets are able to transmit and receive signals modulated and demodulated by the MODEM by using a radio wave in a voice frequency band.
In changing the conversational mode for the data communication mode, generally, the speech signal line is switched while the mobile radiotelephone set is in the off-hook state, and then data communication is started. Accordingly, a special notifying means is necessary to notify the operator of the completion of data communication including abnormal completion of data communication when the data communication mode is changed for the conversational mode upon the completion of data communication. For example, the mobile radiotelephone set is provided with a special tone ringing circuit, and the tone ringing circuit is actuated to generate a tone by a speaker or to flicker an indicator such as a LED upon the change of the data communication mode for the conversational mode. This conventional mobile radiotelephone system, however, requires a special tone ringing circuit or a special indicator to notify the operator of the completion of data communication. The mobile radiotelephone system employing the indicator, in particular, is dangerous because the operator is required to observe the indicator while the operator is driving the mobile vehicle.